Screening of phytotoxic activity and nlp genes from rhizosphere actinomycetes

Abstract

The necrosis and ethylene-inducing peptide (NEP)-like family of proteins [Nep-like proteins (NLPs)] is a recently discovered group of phytotoxins found in a wide range of microorganisms. We screened necrosis activity in actinomycetes isolated from soil samples collected in different provinces of Iran by assaying their fermentation broth bioactivity on the leaves of sunflower (Helianthus annuus). Presence of the nlp gene in the bioactive actinomycete isolates was verified by a pair of degenerated nlp primers. The selected isolates were identified by 16S rRNA gene analysis. Among the 100 actinomycetes screened, 25 isolates were bioactive isolates, of which 12 strains were positive for the nlp gene. Amino acid sequence analysis of the nlp gene revealed that the W residue in the heptapeptide motif “GHRHDWE” was not completely conserved, indicating that the actinomycete NLPs belong to type II. This is the first report on the presence of the nlp gene in rare actinomycetes, including members of Nocardia, Nocardiopsis and Micromonospora, rather than members of the Streptomyces genus.